The present invention relates to an infrared cutoff powder comprising tin-doped indium oxide powder having an infrared cutoff function, an infrared cutoff material in the form of a coating, a film or other shape containing such powder, and a method of manufacturing the same.
This infrared-cutoff powder can cut off infrared rays by more than 90% on the longer-wave side from a wavelength shorter than in the conventional practice, or more specifically, from a wavelength of under 1,000 nm, particularly from a wavelength within a range of from 700 to 900 nm, and is permeable to visible light. It is therefore possible to form from the powder a transparent coating selectively cutting off infrared rays. It can be used, for example, by mixing with cosmetics.
This transparent coating having an infrared ray cutoff effect is useful as a means for preventing forgery of cash cards or other money-substituting papers frequently occurring at present, or as an infrared-ray cutoff coating exerting remarkable effects on the improvement of air-conditioning efficiency. Particularly when used for an ordinary window of housing, a sun-roof, a wall material, or glass for an automobile, this transparent coating displays a remarkable saving of electric power for cooling rooms through cutoff of infrared rays of sunlight in summer, and is applicable as a transparent coating having a high heat-insulating effect in winter. It exerts also a heat-insulating effect on vinyl house farms and hothouses. Furthermore, it is applicable to various products including optical fibers, prepaid cards, sun visors, PET (polyethylene terephthalate) bottles, packaging films, glasses, textile products, peep holes of heating equipment and room-heating appliances and can impart infrared-ray cutoff effects to these products.
As a transparent coating having an infrared-ray cutoff function, which is permeable to a light within the visible region and reflective to light within the infrared region, there are conventionally known: (a) a coating formed on a glass substrate by depositing a thin film of tin-doped indium oxide (hereinafter abbreviated as "ITO") by a vapor deposition method such as physical evaporation, chemical evaporation, or sputtering; (b) an organic coloring matter type near-infrared absorber such as provided by a phthatocyanine group, anthraquinone group, naphthoquinone group, cyanin group, naphthalocyanin group, macromolecular condensation azo group or pyrrole-group, or an organic metal complex of a dithiol group, mercaptonaphthol group or the like, converted into an ink with the use of an organic solvent and an organic binder, which is applied to a substrate, or kneaded with a resin to form a coating, which is laminated on a substrate.
However, said means (a), in which an apparatus requiring a high vacuum or high-accuracy atmosphere control must be used, leads to a high cost and restrictions in size and shape of the coating. Furthermore, it involves such problems as a low capability of mass production and a poor general applicability.
For said means (b), in which the problems of (a) are solved, light transmissivity within the visible region is low, and the coating has a dark color tone such as dark brown or dark blue. In addition, infrared-ray absorption is limited within the near-infrared region of about 690 to 1,000 nm in most cases. When applied to an ordinary window of housing, a roof material for a sun roof, or a wall material, therefore, visibility through a window or glass is low in and outside of the room, with a poor color tone and an insufficient air-conditioning effect in the room.
In view of these problems, (c) a method of forming an infrared-ray absorbing coating has recently been proposed (Japanese Patent Provisional Publication No. 63-281,837), which comprises the steps of preparing a coating material from an organic binder (polyvinyl chloride, an acrylic resin, etc.) and SnO.sub.2 fine particles having infrared-ray cutoff ability and a particle size of from 0.02 to 0.2 .mu.m, an organic solvent (ketone, aromatic group or the like) and a slight amount of dispersant (anionic surfactant) and applying the thus prepared coating material onto a substrate. In order to cause this coating to fully display its infrared-ray cutoff ability, it is necessary to select a coating thickness of at least 12 .mu.m and apply a hot press treatment. A coating thickness of this order results in a low optical transmissivity to visible light of about 50 to 60%, thus impairing transparency.
There is, therefore, an increasing demand for development of a transparent coating having infrared-ray cutoff ability meeting the requirements of the market.